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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

Advancements in an 171 Yb + Optical Clock: From E3 Probing to Inter-Species Comparison

Yuexiang Han, Yani Zuo, Zekun Wang, Shaoyang Dai, Shiying Cao, Fang Fang

Published May 1, 2026• 0 citations
Publisher
DOI
10.1109/ifcs68110.2026.11738350

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Interspecies clock comparison below $5 \times 10^{-18}$ uncertainty with a transportable clock

Chetan Vishwakarma, Ingo Nosske, Tim Lücke +6 more

We report a measurement of the optical frequency ratio between the $^2\mathrm{S}_{1/2}(F=0)$--${^2\mathrm{F}_{7/2}(F=3)}$ electric-octupole (E3) transition of $^{171}$Yb$^{+}$ and the $^1\mathrm{S}_0$--${^3\mathrm{P}_0}$ transition of $^{87}$Sr, $ν_{\mathrm{Yb}^{+}}/ν_\mathrm{Sr} = 1.495\,991\,618\,544\,900\,588\,1(65)$. Reaching a fractional uncertainty of $4.3 \times 10^{-18}$, this result improves upon the previous best by more than a factor of three and is among the few that meet the requirements for interspecies clock comparisons specified by the roadmap towards the redefinition of the SI second. The comparison is between a transportable optical lattice clock and a stationary single-ion clock. It spans a period of nearly two years, during which the transportable clock was intermittently operated off-campus. The ratio was reproducibly measured during four separate campaigns, which are consistent within their statistical uncertainties. The results demonstrate reproducible $10^{-18}$ level operation of the transportable clock and thus validate its application for chronometric geodesy and as a transfer standard for inter-institute clock comparisons, e.g., in the absence of optical fiber links.

physics.atom-phCross-listedarXiv:2608.01916•Aug 4, 2026
We present a scalable mixed-species Coulomb crystal clock based on the ^{1}S_{0}↔^{3}P_{0} transition in ^{115}In^{+}. ^{172}Yb^{+} ions are cotrapped and used for sympathetic cooling. Reproducible interrogation conditions for mixed-species Coulomb crystals are ensured by a conditional preparation sequence with permutation control. We demonstrate clock operation with a 1In^{+}-3Yb^{+} crystal, achieving a relative systematic uncertainty of 2.5×10^{-18} and a relative frequency instability of 1.6×10^{-15}/sqrt[τ/1 s]. We report on absolute frequency measurements with an uncertainty of 1.3×10^{-16} and optical frequency comparisons with clocks based on ^{171}Yb^{+} (E3) and ^{87}Sr. With a fractional uncertainty of 4.4×10^{-18}, the former is-to our knowledge-the most accurate frequency ratio value reported to date. For the ^{115}In^{+}/^{87}Sr ratio, we improve upon the best previous measurement by more than an order of magnitude. We also demonstrate operation with four ^{115}In^{+} clock ions, which reduces the instability to 9.2×10^{-16}/sqrt[τ/1 s].
We present a scalable mixed-species Coulomb crystal clock based on the S01↔P30 transition in In+115. Yb+172 ions are cotrapped and used for sympathetic cooling. Reproducible interrogation conditions for mixed-species Coulomb crystals are ensured by a conditional preparation sequence with permutation control. We demonstrate clock operation with a 1In+-3Yb+ crystal, achieving a relative systematic uncertainty of 2.5×10-18 and a relative frequency instability of 1.6×10-15/τ/1 s. We report on absolute frequency measurements with an uncertainty of 1.3×10-16 and optical frequency comparisons with clocks based on Yb+171 (E3) and Sr87. With a fractional uncertainty of 4.4×10-18, the former is - to our knowledge - the most accurate frequency ratio value reported to date. For the In+115/Sr87 ratio, we improve upon the best previous measurement by more than an order of magnitude. We also demonstrate operation with four In+115 clock ions, which reduces the instability to 9.2×10-16/τ/1 s.
Interspecies clock comparison below 5×10−185 \times 10^{-18}5×10−18 uncertainty with a transportable clock
We report a measurement of the optical frequency ratio between the 2S1/2(F=0)^2\mathrm{S}_{1/2}(F=0)2S1/2​(F=0)--2F7/2(F=3){^2\mathrm{F}_{7/2}(F=3)}2F7/2​(F=3) electric-octupole (E3) transition of 171^{171}171Yb+^{+}+ and the 1S0^1\mathrm{S}_01S0​--3P0{^3\mathrm{P}_0}3P0​ transition of 87^{87}87Sr, νYb+/νSr=1.495 991 618 544 900 588 1(65)ν_{\mathrm{Yb}^{+}}/ν_\mathrm{Sr} = 1.495\,991\,618\,544\,900\,588\,1(65)νYb+​/νSr​=1.4959916185449005881(65). Reaching a fractional uncertainty of 4.3×10−184.3 \times 10^{-18}4.3×10−18, this result improves upon the previous best by more than a factor of three and is among the few that meet the requirements for interspecies clock comparisons specified by the roadmap towards the redefinition of the SI second. The comparison is between a transportable optical lattice clock and a stationary single-ion clock. It spans a period of nearly two years, during which the transportable clock was intermittently operated off-campus. The ratio was reproducibly measured during four separate campaigns, which are consistent within their statistical uncertainties. The results demonstrate reproducible 10−1810^{-18}10−18 level operation of the transportable clock and thus validate its application for chronometric geodesy and as a transfer standard for inter-institute clock comparisons, e.g., in the absence of optical fiber links.